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![Stream, Robert Sibley Volcanic Preserve, Orinda, California. Click to see 800x600. [C-2000Z]](http://dpfwiw.com/images/stream.jpg)
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Paul Saunders' PhotoShop Post-Processing Tips
Paul's valuable tips cover 3 important areas in the post-processing of outdoor color images:
Since I can't improve on Paul's words, I've quoted them nearly verbatim—with his permission, of course. Note that these PhotoShop tips are easily ported to other advanced image processors like Corel PHOTO-PAINT. Hopefully they'll inspire you to get to work on your photos with whatever tools you have.
And now, here's Paul...
Tone Curves
...give the [PhotoShop] Curves tool a try. It's the single most powerful feature of Photoshop in my opinion....
When I first tried Curves I hated it, probably because I was overdoing it. The key is to make tiny adjustments. Load any pic into Photoshop, select Curves (Control+M), and click twice on the line to make two control points, one near the top and one near the bottom. Move the top one up slightly, and the bottom one down slighty, to make a very gentle "S" shape curve. Notice the instant dramatic improvement! The beauty of this tool is that it increases contrast without over or under-exposure.
Make tiny adjustments and see the huge differences they
make. The key is not to overdo it. You have to be very precise with
the mouse.
Then change the colour channel from RGB to blue. Click once in the centre of the line and move it slightly down and to the right. This adds yellow and improves virtually any picture you care to try it on. I do this with practically every pic and it's usually the only colour adjustment I make. The reason is simple, most photos have a strong blue component, so a little yellow cancels it out and gives the pic a much warmer feel. It works especially well with pics taken on cloudy days.
Of course you can add yellow with any photo program, but you can take it one stage further, by applying an "S" shaped curve on a colour channel. Let's say you add yellow to a photo taken on a nice sunny day with a deep blue sky. The addition of yellow will improve the look of the ground but will compromise the blue of the sky, making it appear duller. By applying an "S" shaped curve to the blue channel, you can add yellow to the darker ground whilst simultaneously adding blue to the lighter sky thus enhancing it.
You can even go further and place three points on a curve. This is where it becomes very tricky. I haven't really mastered 3-point curves yet, but I'm getting better at them.
![Before and after color rebalancing with the PhotoShop Curves feature. Click to see 750 x 500 version. [Paul Saunders]](http://dpfwiw.com/images/befaft.jpg)
The
[image at right] was one of the most difficult pics I've ever
worked with. I used a 3-point curve on the RGB channel and 2-point
"S" curves on all three colour channels. I spent about
an hour balancing that pic, trying to recreate reality. Most pics
take me about two minutes.
Anyway, give Curves a try. You should be quite surprised at what you can achieve. (Don't give up on the first attempt.) ...
Sharpening
Sharpening should only be done once, and it should be the very last thing you do.
I typically work on an image at a large size, archive it, then shrink it to the size I need and sharpen it once. Sharpening usually improves the land but makes clear skies look grainy. Lots of interesting cloud detail can benefit from it. In the case of clear skies, I first sharpen the picture, then use the history feature to go back one step, select the history brush, tick the sharpened step and then "paint" the sharpened picture over the land area but not the sky.
JPEG Compression
For internet use, I recommend saving images initially as high quality JPEGs, then loading them into JPEG Optimizer and re-saving them. I highly recommend this program. It shrinks the file to an extremely small size with remarkably little loss of quality. The best thing is that you can see how it's going to look before you save it, so you can play about with the settings until you find the best compromise between quality and file size.
—Paul Saunders, Wilderness Wales
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Sharpening in Post-Processing
Paul Saunders touched on sharpening above. Here we explore it more detail.
All digital camera images benefit from sharpening. The Bayer color interpolation process and the anti-aliasing filters used in single CCD cameras guarantee that. Many digital cameras enable in-camera sharpening by default for that very reason. Letting the camera do the sharpening may be smart for shots from the office picnic, but for shots that count, you'll generally be better off saving sharpening for post-processing. Why?
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To avoid artifacts, sharpening should always be the very last step in the post-processing sequence, even after resampling to printer resolution.
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To maintain precise control over the delicate sharpening process, do it yourself.
That said, many cameras do a decent job at sharpening.
Unsharp Masking
Of all the commonly available sharpening tools, unsharp masking (USM) gives you the most control and generally produces the best results, but its use remains something of a black art as inscrutable as its name, which derives from the darkroom technique upon which it's based. Different subjects require different USM approaches, and experts offer widely varying tacks, but everyone agrees that USM is easy to overdo, and that results can be monitored safely only at 100% image size. Whenever possible, convert to Lab color mode and sharpen only the luminance or lightness channel after resampling to final image size and resolution.
Most USM implementations require 3 parameters:
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intensity, percentage or amount (0-500%)—the overall intensity of the sharpening effect
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radius (0-20)—the distance in pixels over which contrasts are to be enhanced
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threshold (0-255)—the minimum contrast difference to which USM will be applied
Note: The ranges shown are those available in Corel PHOTO-PAINT 9.
The choice of radius is particularly dependent on image content and tends to vary directly with the size of the image features you're most interested in sharpening. Visually fine-tuning radius for the image at hand at overly high intensity before reducing intensity to taste is a very reasonable approach. Others prefer to start with a radius equal to final image resolution (in PPI, not DPI) divided by 150-200. Still others advocate repetitive USM applications at very small radius and high intensity (e.g., 0.2 at 400%). Thresholds in the 1-10 range are common, but some prefer 0 while others generally stay above 4. Large-radius, low-intensity USM (e.g., 20 at 20%) finds use in enhancing contrast and eliminating haze without exaggerating whites and blacks, but it produces little if any discernable sharpening.
Bruce Fraser's sharpening tutorial for PhotoShop is by far the best I've seen, but Michael Reichmann's Instant PhotoShop tutorial may be a better place to start. Fraser's article begins with solid USM advice and then extends the underlying concepts to ever more powerful sharpening techniques using adjustment layers and Lab color. Fred Miranda's selective sharpening approach is also well worth examining. All these PhotoShop methods are readily ported to Corel PHOTO-PAINT.
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Editor's Notes
Thanks for a great leg-up on a challenging topic, Paul. Be sure to visit Paul's Wilderness Wales website to see the spectacular Welsh landscapes he's produced from scanned 35 mm slides using precisely the post-processing techniques he's detailed above.
JPEG Compression
You'll find additional information on JPEG compression, JPEG artifacts and related issues elsewhere on this site.
Editing in the Lab Color Space
For color images, a very useful variation on Paul's approach takes advantage of the clean separation of luminance (brightness) and chrominance (color) data available in the Lab color space, a powerful alternative to the more familiar RGB color space. Try converting your RGB images to Lab color mode before editing. Then apply tone curves separately to the L (luminance, lightness) and b (yellow-blue) channels. Sharpen only to the L channel using unsharp masking technique for maximum control, taking care not to oversharpen, particularly if in-camera sharpening is enabled. (It's usually on by default.) To save your work as a JPEG, you'll have to convert back to the RGB color mode at the end, but the entire RGB -> Lab -> RGB transformation is quick and lossless.
Michael Cervantes' practical PHOTO-PAINT Lab color tutorial, The Magic of Lab Color Space, is a great introduction to the miracles one can work with Lab-based photo editing.
B&W Editing
Editing images for black-and-white (B&W) output usually starts with a well-executed conversion from color to grayscale. From there, tone curves and sharpening play critical roles.
For a leg up on B&W post-processing, see the dpFWIW digital B&W article, particularly the sections on grayscale conversion using Lab mode and channel mixing.
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References and Links
(See also the home page links.)
Luminous Landscape—Michael Reichmann's masterful site bills itself as "the web's most comprehensive site devoted to the art of landscape and nature photography using digital imaging techniques." I couldn't agree more. Scanned film images are the usual raw materials here, but from there on, it's pure DP gold—especially the PhotoShop tutorials, which can usually be ported to any competent editor.
The Magic of Lab Color Space—Michael Cervantes' practical PHOTO-PAINT Lab color tutorial is a great introduction to the miracles one can work with Lab-based photo editing.
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Unless explicitly attributed to another contributor, all content on this site © Jeremy McCreary
Comments and corrections to Jeremy McCreary at dpFWIW@cliffshade.com, but please see here first.
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